This invention relates to serial communications interfaces, and more particularly, to ways in which to initialize serial communications links between integrated circuits such as programmable logic devices.
Serial communications formats are often used in modern electronics systems. Serial communications can be faster than parallel communications, use fewer pins, and, particularly when differential signaling schemes are used, can have higher noise immunity.
It can be challenging to handle serial data streams at high data rates (e.g., at data rates above several Gbps). As a result, it is often advantageous to support high-speed serial data communications using multiple smaller serial data paths operating in parallel. These smaller serial data paths are often referred to as “lanes.”
Before two integrated circuits can communicate over a single-lane or multi-lane serial link, the link must be initialized. The initialization process involves handshaking operations between the circuits to ensure that the link is set up properly. The type of handshaking operation that is used during link initialization depends on the type of serial communications protocol being used for the link. With some communications protocols, it is possible to check the link for problems such as inadvertently reversed conductors (polarity reversal) and improperly ordered lanes (lane reversal) during link initialization. When available, these checking procedures can help reduce errors and ensure proper operation of a link.
Because it takes a certain amount of circuit resources to implement lane initialization features such as automatic polarity reversal and lane order reversal, a logic designer may not always desire to include these features in a design. However, these features may be mandated by the serial communications protocol being used. If the designer is not willing to commit on-chip resources for implementing these features, the designer must either risk creating a non-compliant design that violates the protocol being used or must use a serial communications protocol that never allows for the use of automatic polarity or lane order reversal.